Plastic Scintillation and dryness evaporation: a new ... scintillation and dryness evaporation: a new procedure for alpha/beta activity determination in ... Plastic scintillation and

B. Aboudou, H. Bagán, A.Tarancón, G.Rauret, J.F Garcia. Plastic scintillation and dryness evaporation: a new procedure for alpha/beta activity determination in water samples

Plastic Scintillation and dryness evaporation: a new procedure for Alpha/Beta determination in water

samples

Bouchra Aboudou, Hector Bagán, Alex Tarancón Sanz, Gemma Rauret, Jose Francisco García

Departmento de Química Analitica de la Universidad de Barcelona, Spain

LSC 2010 Advances in Liquid Scintillation SpectrometryParis, France, 6-10 September 2010


Plastic Scintillation and dryness evaporation: a new procedure for Alpha/Beta determination in water samples

Introduction

- Gross Alpha/Beta are an important parameters to monitorize the radioactivity in water

Depending on the level, specific analysis are required.

- Procedures to determine Gross Alpha/Beta activity.

. Proportional counters: sample evaporated to dryness and deposited on a planchet.- Well established- Low detection efficiency

. Liquid Scintillation Counting: sample mixed with scintillation cocktail (PSA).- High detection efficiency- Amount of sample? Mixed waste production.



Introduction

- Plastic Scintillation is an alternative method to liquid scintillation.

. In general, sample solution is added to a vial filled up with plastic microspheres (PSm)- High detection efficiency (except for low beta emitters)No limited amount of sample No mixed waste production.

- New procedure for Gross Alpha/Beta determination by Plastic Scintillation:

. Water sample evaporated to dryness on the PSm inside the counting vial

. Measurement in a Scintillation counter (PSA).



Objective

To evaluate the capability of the new procedure based on Plastic Scintillation and dryness evaporation to the determination of gross Alpha/Beta parameters in aqueous samples.

(Partially achieved)



Experimental

Apparatus and reagents.

- Detector Quantulus liquid scintillation (EG&G Wallac)- Poliethylene vials (20 ml) from Packard Instruments Co.- Plastic Scintillation microspheres (Detec-Rad)

diameters (120-180, 400-500 and 630-800 µm)- Active solutions: 90Sr/90Y, 14C and 241Am

Sample preparation procedure:

• 20 ml scintillation vial• 2 g of PSm• 1-20 ml of solution (1 ml)• Evaporate to dryness at 40ºC• Measurement

40ºC



Results and discussion – optimum conditions determination

Optimum conditions determination.

- Liquid Scintillation vs Plastic Scintillation vs Plastic Scintillation+ dryness evaporation

- Infuence of the PSm diameter.

- Influence of the beta emitter energy.

- Influence of sample volume




Liquid Scintillation vs Plastic Scintillation vs Plastic Scintillation+ dryness evaporation.

Conditions: PSm (630-800 µm), 90Sr/90Y – 241Am

241Am

LS -> PS: higher distance – lower energy – shorter pulse – PSA shifts to lower valuesPS -> PS+dryness : intermediate.






241Am

Detection Efficiency: PS 27.6 – PS+dryness evaporation 99.3 %


0 200 400 600 800 1000 1200-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

channels

Eff

(%)

CLCPCP evap






90Sr/90Y







90Sr/90Y

Detection Efficiency: PS 163.2 – PS+dryness evaporation 190.5 %


0 200 400 600 800 1000 12000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

channels

Eff

(%)

CLCPCP evap










PS+ dryness evaporation. – Influence of the PSm diameter

Conditions: PSm (120-180, 400-500, 630-800 µm), 90Sr/90Y – 241Am

241Am

PSm diameter increase: total surface decreases – available surface increases?

thinner recovery layer - higher energy – longer pulses - PSA shifts to higher values






241Am



Diameter

With solution Evaporated

Eff±STD Eff±STD120-180 D1: 59,6 ± 0,9 D1: 101,5 ± 1,3

400-500 D3: 41,1 ± 0,7 D3: 101,7 ± 1,3

630-800 D4: 27,6 ± 0,8 D4: 99,3 ± 1,3

0 200 400 600 800 1000 1200-0.2

0

0.2

0.4

0.6

0.8

1

1.2

channels

Eff

(%)

120-180400-500630-800






90Sr/90Y








90Sr/90Y



Diameter


Eff±STD Eff±STD120-180 D1: 178,2 ± 3,4 D1: 191 ± 6,8

400-500 D3: 173,5 ± 2,6 D3: 192,7 ± 2,5

630-800 D4: 163,2 ± 2,3 D4: 190,5 ± 2,9

0 200 400 600 800 1000 12000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

channels

Eff

(%)

120-180400-500630-800






Proposed diameter: higher (630-800 µm)




PS+ dryness evaporation. – Influence of beta emitter energy

Conditions: PSm (120-180, 400-500, 630-800 µm), 14C (156 keV) - 90Sr/90Y ( 2.27 MeV)

14C 90Sr/90Y






PS+ dryness evaporation. – Influence of beta emitter energy

Conditions: PSm (120-180, 400-500, 630-800 µm), 14C (156 keV) - 90Sr/90Y (2.27 MeV)

14C 90Sr/90Y

Low-Medium energy beta emitters can be detected with high efficiency

Diameter


Eff±STD Eff±STD120-180 D1: 39,7 ± 0,8 D1: 80,3 ± 1,1

400-500 D3: 25,4 ± 0,6 D3: 78,5 ± 0,7

630-800 D4: 18,3 ± 0,6 D4: 78,3 ± 1,1

0 200 400 600 800 1000 1200-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

channels

Eff

(%)

120-180400-500630-800

0 200 400 600 800 1000 12000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

channels

Eff

(%)

120-180400-500630-800




PS+ dryness evaporation. – Influence of the sample volume

Conditions: PSm (630-800 µm)Solution volumes: 1, 5, 20 ml.

Calibration procedures:

• Comprimise PSA: 90• Double PSA: 120 - no 90Sr/90Y at α spectrum (quantification 241Am)

60 - no 241Am at β spectrum region (quantification 90Sr/90Y)

Detection efficiency is not constant with sample volume change (material deposited) -> calibration in progress.

Compromise PSA 90Sr/90Y 241Am

Volume Eff β Eff α

1 ml 161.98±2.32 84.27±1.84

5 ml 163.21±2.74 76.38±0.73

20 ml ‐ ‐

Double PSA 90Sr/90Y 241Am

Volume Eff β Eff α

1 ml 110.92±2.20 47.35±2.42

5 ml 117.43±4.23 41.38±1.00

20 ml ‐ ‐



Results and discussion – sample quantification (exploratory results)

PS+ dryness evaporation.

Conditions: PSm (630-800 µm)

Calibration: Constant EfficiencyVolumes: 5 ml.

Drinking water (Fontvella) (3 Replicates).

Exploratory Relative Errors in Gross Alpha/Beta Compromise PSA > Double PSAExploratory Relative Errors - Double PSA < 12% (except proportion 1:4)

Act Sr Act Am Prop compromise Double PSA

Err Sr Err Am Err Sr Err Am

17.91 38.23 1:1 -28.92±4.30 -5.20±3.28 -3.53±1.61 -2.17±3.02

36.54 38.48 2:1 -15.45±2.01 -9.59±3.87 4.62±4.12 -1.02±3.60

18.14 71.67 1:2 -49.52±5.62 -5.44±3.06 -9.12±3.33 -1.53±2.16

75.10 38.64 4:1 -9.66±2.37 -19.83±1.50 5.11±4.40 -5.67±3.08

18.13 154.56 1:4 -106.46±5.85 -3.33±0.95 -36.10±8.32 -1.85±3.90



Conclusions

- A new procedure for Alpha/Beta determination in water samples is defined based on the use of plastic scintillator microsphere and dryness evaporation.

- Evaporated water samples on PSm produce:. pulses of intermediate energy between LS and PS. pulses of intermediate duration between LS and PS. spillover vs PSA distribution shifted to lower values

- Changes in the PSm diameter produce slight changes in spillovervs PSA distribution.

- Low energy beta emitters are detected with high efficiency.

- Detection efficiency depends on the material deposited (calibration is required)

- Exploratory results using using constant efficiency and double PSA allow Gross Alpha / Beta activity determination with relative errors < 12 %



Acknowlegments

. Ministerio de Ciencia e Innovación (Spain) for Financial support (CTM2008-01147).

Plastic Scintillation and dryness evaporation: a new procedure for Alpha/Beta determination in water

samples

Bouchra Aboudou, Hector Bagán, Alex Tarancón Sanz, Gemma Rauret, Jose Francisco García

Departmento de Química Analitica de la Universidad de Barcelona, Spain

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Plastic Scintillation and dryness evaporation: a new ... scintillation and dryness evaporation: a new procedure for alpha/beta activity determination in ... Plastic scintillation and